In addition to your self-monitoring routine, you'll be donating quite a bit of blood to the testing cause at your doctor's office or lab. One of the most important of these tests is the glycosylated hemoglobin test (also called a glycated hemoglobin test, GHB, or HbA1c). The A1C assesses your long-term, three-month glucose average.

Glycosylated hemoglobin is a substance produced when excess glucose attaches itself to hemoglobin (a substance in red blood cells). The higher your percentage of glycated hemoglobin, the higher your blood glucose levels were over the past ninety-day period.

The ADA recommends that an A1C be performed at least twice annually, and up to four times a year for individuals who are undergoing adjustments to treatment or failing to meet treatment goals. Patients who use insulin to control their type 1 or type 2 diabetes should have the test performed quarterly as well. Pregnant patients with pre-existing type 1 or type 2 diabetes will probably have more frequent A1C tests at four- to six-week intervals.

Long-Term Control

A1C levels are the best measure of how you're doing in the long term. While home monitoring offers you a single snapshot of where your blood sugar is at a particular point in time, an A1C test is like a surveillance camera running for three months, day and night, giving you an overview of your average blood glucose levels.

The Diabetes Control and Complications Trial (DCCT), a landmark clinical study that took place in medical centers across the United States in the early 1990s, demonstrated that people with type 1 diabetes were 40 to 75 percent less likely to develop neuropathy, retinopathy, and nephropathy (kidney disease) when they kept their A1C values at an average of 7.2 percent (achieved through an “intensive care” routine of testing four times daily, keeping in close contact with care providers, and participating in diabetes education courses).

Follow-up studies of DCCT participants also found that tight control of blood glucose reduced the risk of atherosclerosis (as measured by carotid artery-wall thickness), a benefit that remained six years after the DCCT concluded.

Similarly, the United Kingdom Prospective Diabetes Study (UKPDS), another large-scale study, found that participants with type 2 diabetes who kept their A1C values below 7 percent had a 25 percent reduction in the incidence of these same complications. And for every percentage point decrease in A1C achieved, there was a 35 percent reduction in the risk of complications. Whether you have type 1 or type 2 diabetes, the A1C not only looks back at the past three months but also provides a glimpse into your future risk of complications.

Determining Your Target Goal

People without diabetes have an A1C of around 5 percent. It is possible for people with well-controlled diabetes to achieve A1C levels in a range very close to normal. The American Association of Clinical Endocrinologists (AACE) recommends that individuals with diabetes try to achieve a target A1C of 6.5 percent or less to minimize the risk of long-term complications.

The American Diabetes Association (ADA) suggests an A1C goal of less than 7 percent for the general diabetes population, although it acknowledges that “selected individual patients” can strive for a goal of 6 percent or lower. This does not include children, who are considered vulnerable to the effects of hypoglycemia and may have slightly higher A1C goals.

The DCCT and UKPDS both found that the closer to normal you can bring your A1C, the lower your risk for microvascular complications. But don't be discouraged if your initial A1C tests are higher. Target A1C levels are as individual as diabetes itself. Your doctor will look at your medical history, age, lifestyle, and other factors, and will work with you to define a custom target goal specific to your needs.

It can take some time to get your A1C where you want it. In the UKPDS, the average A1C at time of type 2 diagnosis was 9.3 percent, which leaves a lot of room for improvement.